Flower morphology is one of the critical factors in ornamental value of garden plants. The development of a flower begins with differentiation into a flower primordium from an inflorescence meristem. From the floral meristem contained in the flower primordium, four types of flower organs, sepals, petals, stamens and pistils are differentiated. Thereafter, a mature flower is formed as a complex organ containing differentiated flower organs. Plants with modified flower morphology are highly useful in agriculture because they can be utilized in creation of novel garden plants and creation of fruits with a novel morphology.
Thus far, modification of flower morphology of a plant has been generally carried out by cross-breeding in which varieties of plants are crossed. Yet, the conventional cross-breeding requires long periods of time and expertise in order to produce a plant having the intended morphology. Therefore, a method for simply and surely modifying the flower morphology is demanded.
In general, development of flower morphology in higher plants is explained by the ABC model. In this model, it is considered that the flower morphology is modified through transcriptional regulation of Class A, Class B and Class C genes belonging to a MADS-box family (Hajime Sakai, Molecular genetics of flower morphogenesis, new edition “Molecular mechanisms of form determination in plants” (Shujunsha) 150-163 (2000)). The MADS-box family genes are genes encoding a transcription factor containing a conserved region called the MADS-box and constitute a gene family composed of 30 or more genes. Examples of the transcription factor include the Class A genes such as APETALA1 (AP1) and APETALA (AP2), the Class B genes such as APETALA3 (AP3) and PISTILLATA (PI) and the Class C genes such as AGAMOUS (AG). Changes in the flower morphology have been confirmed in mutants of these genes.
Meanwhile, a fundamental structure of a leaf of angiosperms, which is relatively flat tissue, can be generally explained in the basis of three axes, namely the proximal-distal, central-lateral and adaxial-abaxial axes. Examples of transcription factors to determine these polarities include the YABBY group such as YABBY1 (YAB1) or YABBY3 (YAB3), the HD group such as PHABULOSA (PHB) and the KANADI group such as KANADI (KAN). It has been known that these factors are involved in determination of the polarity in leaf blades (Non-patent Literatures 1 to 3).
As a method for modifying flower morphology by genetic engineering, the present inventors have thus far found a method using a peptide which converts an arbitrary transcription factor into a transcription repressor (for example, Patent Literatures 1 to 7). This peptide is excised from a Class II ERF (Ethylene Responsive Element Binding Factor) protein or a plant zinc finger protein (for example Arabidopsis thaliana SUPERMAN protein or the like) and has an extremely simple structure. And, by introducing a gene encoding a fusion protein (chimeric protein) in which various transcription factors are fused with the above-mentioned peptide into a plant, a transcription factor had been converted to a transcriptional repressor, and the present inventors have successfully produced a plant in which expression of a targeted gene whose transcription is promoted by the transcription factor is suppressed. Specifically, the present inventors have established a method for producing a male-sterile plant and a method for modifying flower morphology, both in which the expression of the AP3 gene or AG gene of Arabidopsis thaliana, which gene is the above-mentioned MADS-box family gene, is suppressed by using a repressor capable of binding to a promoter region of the respective gene (Patent Literatures 8 to 9).
However, it is not known that the flower morphology is modified by overexpressing a chimeric repressor in a recombinant plant so as to suppress the function of a transcription factor involved in the polarity determination of a plant organ, which chimeric repressor was obtained by converting the transcription factor (YAB1, KAN or NIB) involved in the polarity determination of a plant leaf into the transcription repressor.    Patent Literature 1: JP 2001-269177 A (disclosed on Oct. 2, 2001)    Patent Literature 2: JP 2001-269178 A (disclosed on Oct. 2, 2001)    Patent Literature 3: JP 2001-292776 A (disclosed on Oct. 2, 2001)    Patent Literature 4: JP 2001-292777 A (disclosed on Oct. 23, 2001)    Patent Literature 5: JP 2001-269176 A (disclosed on Oct. 2, 2001)    Patent Literature 6: JP 2001-269179 A (disclosed on Oct. 2, 2001)    Patent Literature 7: WO03/055903 (disclosed on Jul. 10, 2003)    Patent Literature 8: JP 2005-192483 A (disclosed on Jul. 21, 2005)    Patent Literature 9: JP 2006-42729 A (disclosed on Feb. 16, 2006)    Non-patent Literature 1: Eshed Y, Baum S F, Perea J V, Bowman J L. Curr Biol. 2001 Aug. 21; 11(16):1251-60.    Non-patent Literature 2: Eshed Y, Izhaki A, Baum S F, Floyd S K, Bowman J L. Development 2004 June; 131(12):2997-3006.    Non-patent Literature 3: Kidner C A, Timmermans M C. Curr Opin Plant Biol. 2007 February; 10(1):13-20